Polyoxotungstate ligands

Although terminal oxo complexes of the late-transition-metal elements have been proposed as possible intermediates for oxidations catalyzed by these elements, late-transition-metal-oxo complexes were scarcely known. Hill and coworkers reported the synthesis and characterization of Pt4 + -, Pd4 + - and Au3 + -oxo complexes, [M(0)(0H2) W0(0H2) (PW9034)2]m (M = Pt, Pd and Au, n = 0-2), stabilized by electron-accepting polyoxotungstate ligands [109-111]. The stoichiometric reaction of the Au-oxo complex [Au(0)(0H2) W0(0H2) 2 (PW9034)2]9 with triphenylphosphine led to the formation of triphenylphosphine oxide. 

So, NMR spectra of 4,4 -bipyridyl, pyrazine, and ethylenediamine coordinated to undecatungstocobalto(III)silicate and -borate anions. Identification of 1 1 and dumbbell-shaped 12 complexes, Bull. Korean Chem. Soc, 14 759 (1993) (c) J.L. Samonte and M.T. Pope, Derivatization of polyoxotungstates in aqueous solution. Exploration of the kinetic stability ofcobalt(II)- and cobalt(III) derivatives of lacunary anions with pyridine and pyridine-type ligands. Can. J. Chem.. In press... 

A mechanistic study has revealed a weak electrophilic character for the competent oxidant, turning to a biphilic nature with respect to sulfoxide oxidation. This behavior is likely to be stimulated by the polynuclear framework, which may foster a dual activation of both the oxidant and the sulfoxide by coordination to proximal Lewis acid sites on the polyoxotungstate surface. The postulated asymmetric binding of the peroxo-ligand, not evolving to a bidentate j -coordination mode, could explain the atypical selectivity behavior, with respect to classical d -peroxometal complexes. 

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